Aptitude - Time and Work - Discussion

Still I have confusion. How 7/60 comes?

Hi friends,

A's 1 day work=1/15; B's 1 day work=1/20
OK.Then we calculate how much A + B can do in 1 day.
ie 1/15 + 1/20 ( in fraction if denominator is different first we find the l.c.m of denominator).so we calculate the l.c.m of 15 and 20 ie 60(15 and 20 is divided by 5 we get the answer 3 and 4 so we find l.c.m by multiplying 5*3*4=60).1/15*60+1/20*60=4+3/60=7/60.
if A and B do work in 4 days=7/60*4=7/15

Remaining work=1-7/15 = 8/15 [ (15*1-7)/15 = 8/15 ].

1/50+1/20) = (20+15)/300 //This get by cross multiplication.

= 35/300

= 7/60.
why we should Division do for (20+15)/300, how did the 300 is come?

Thanku Prakash :).

Very simple,
15+20=35
15*20=300
35/300=7/60
work is 1 so=1-7/15
=15-7/15
Ans is = 8/15

35/300=7/60 please explain it.

Can you explain how did 7/60 come?

Hi Manoj,

You need to simplify big number 35/300 in to small number for further calculation.

So, you need to divide one common number of both numerator and denominator.

You couldn't select 2, 3 and 4 as a dividing number. But you can use 5 as a common divider.

If you divide 5 in both numerator and denominator, you will get 7/60.

I hope your doubt clarified.

"A" can can do a work in 15 days therefore he did 1/15 of the work in a day.
"B" can do the same work in 20 days therefore he did 1/20 of the work in a day.

Therefore.

[1/15 + 1/20]4 = [4/60 + 3/60]4.

[7/60]4 = 7/15 of the work done.

The total work left = 1 - 7/15 = 15 - 7/ 15 = 8/15.

Good explanation anshu.